1. Field of the Invention
The present invention relates to an information recording method, and in particular, to an information recording method carrying out recording of data by a vertical magnetic system onto an information recording medium on which servo information for tracking is magnetically pre-format-recorded.
2. Description of the Related Art
Accompanying the rapid increase in the amount of information handled by personal computers, information recording media, which have a high capacity, are inexpensive and whose access time is short, have been developed one after another. Examples of such high-capacity information recording medium include a built-in type magnetic recording medium such as a hard disk, a removable magnetic recording medium such as a ZIP drive developed by Iomega Corporation, and the like. In the hard disk and ZIP, endowing the medium with a large capacity is realized by enlarging the track density by narrowing the width of the tracks. In order to playback a recording signal at a satisfactory S/N ratio by accurately scanning a magnetic head on the narrow tracks, a tracking-servo technology, which detects the relative offset between the magnetic head and the track and corrects the position of the magnetic head, performs an important role.
On a hard disk and a ZIP drive, a servo signal for tracking, an address information signal, a reading clock signal, and the like are recorded (pre-format-recorded) with high positional accuracy in advance at the time of manufacturing the magnetic recording medium. The regions (servo regions) at which these signals are recorded are discretely disposed with respect to the surface of the disk. The magnetic head accurately scans the tracks while checking and modifying its position by reading these signals.
On the other hand, currently, the magnetic recording system adopted in hard disk devices on the market is a longitudinal magnetic recording system carrying out magnetization in the scanning direction of the recording medium. However, due to “thermal decay” (super paramagnetic effect) in which the magnetized information recorded on the medium is erased by heat, there are limits to making the medium high density. In contrast, a vertical magnetic recording system carrying out magnetization perpendicular to the disk surface of the recording medium is anticipated as the next-generation magnetic recording system that realizes high densification. As a magnetic material for vertical magnetic recording, a cobalt chrome alloy (CoCr) is considered to be effective.
In a hard disk device, the magnetic head flies above the surface of the magnetic disk in accordance with the rotation of the magnetic disk, and carries out magnetic recording without contacting the surface. Hence, the magnetic head and the magnetic disk are prevented from contacting one another at the time of high-speed rotation, and the magnetic disk is prevented from being broken due to the shock such contact would cause. Accompanying the advance of high densification, the flying height of the magnetic head (The distance between the magnetic head and the surface of the magnetic disk) has been gradually decreased. By using a magnetic disk on which a magnetic recording layer or the like is formed on an extremely smooth glass substrate whose mirror surface has been polished, currently, a floating height of 10 nm to 20 nm has been realized.
However, although the track width is narrowing with the advance of further densification, in a conventional servo system in which servo signals are written by being dispersed at intervals, a problem arises in that the magnetic head cannot accurately scan (servo-follow) the tracks. In particular, at a recording density of more than 20 gigabits/inch2, the probability that problems will arise in servo-following is high.
Further, in accordance with the above-described vertical magnetic recording system, although further densification can be attempted, there is the problem that, if the densification progresses, the individually recorded signals become weak and playback gradually becomes more difficult. Therefore, if high density recording is to be carried out with the vertical magnetic recording system, the readability must be improved by further shortening the distance between the magnetic head and the magnetic disk, or the like.